1. Field of the Invention
The invention relates to a wireless receiver and, more specifically, to a wireless receiver required to match a time reference on a reception side with a time reference transmitted from a transmission side.
2. Description of the Related Art
Generally, the moving picture experts group/moving picture image coding experts group (MPEG) standard is known as one of an internationally standardized information source coding systems for compressing/decompressing color moving images. In MPEG, MPEG-2, which applies to a high-quality moving picture such as digital direct broadcasting by satellite and DVD-video, and MPEG-4, which is a moving picture system capable of coding with a low bit rate for utilization in a mobile communication, cellular phone, personal handy-phone system (PHS), and analog telephone network are known. Digital broadcasting such as DBS digital broadcasting and terrestrial digital broadcasting and MPEG-2 transport stream (TS) system corresponding to a TS suitable for digital communication, etc., are known as one of the stream formats of MPEG-2. A general configuration of MPEG-2 TS system is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 10-206570. MPEG-2 TS system uses a transmission format in which data such as compressed video/audio is divided into TS packet units with a fixed length of prescribed bytes.
A conventional MPEG-2 TS system used for digital television broadcasting uses a voltage-controlled crystal oscillator (VCXO). The VCOX generates a reference clock signal of 27 MHz. The clock signal output from the VCXO is supplied to an NTSC encoder and a phase-locked loop circuit for an audio clock. A conventional phase-locked loop circuit for the audio clock uses an analog circuit to convert the supplied reference clock signal of 27 MHz into a master clock signal to be used for an audio digital-to-analog converter at the time of reproduction of an audio signal.
The master clock signal used at the audio digital-to-analog converter is different in specification thereof, and it has a frequency of 256 times or 284 times as high as the sampling frequency. For example, in the case where the sampling frequency is the normal 48 kHz, if the master clock signal has a frequency 256 times as high as the sampling frequency, the frequency of the master clock signal becomes 12.288 MHz. Frequency accuracy of the master clock signal used at the audio digital-to-analog converter is generally about ±5%. Frequency accuracy of the reference clock signal of 27 MHz used for an NTSC converter is different in specification thereof, and about ±5%. As stated above, the clock signal used in the conventional MPEG-2 TS system requires high frequency accuracy.
In recent years, digital television broadcasting has been planned for mobile equipment. A mobile terminal to receive the digital television broadcasting supplies a reproduced video signal to a display device as it is without converting it into the NTSC standard and can display images. Accordingly, the NTSC encoder is not required and the reference clock signal of 27 MHz with high accuracy to be supplied to the NTSC encoder is also not required. On the other hand, the master clock signal to be supplied to the audio digital-to-analog converter still requires high accuracy. However, if an audio master clock signal is not synchronous with the reference clock signal of 27 kHz, an acquisition failure of data at the audio digital-to-analog converter occurs.
As described above, the mobile terminal of the digital television broadcasting for mobile equipment can eliminate the VCXO for generating the reference clock signal of 27 MHz with high accuracy and reduce cost. However, if the VCOX is eliminated, because of reduction in frequency accuracy of the audio master clock signal, degradation in sound quality such as disturbance of sound occurs and because of non-synchronization of an audio master clock signal with the reference clock signal of 27 kHz, the acquisition failure of the data at the audio digital-to-analog converter also occurs.